For decades, airlines have worked to find new ways to fit as many seats as possible on their aircraft, a trend that hasn’t let up even as carriers are coming off a stretch of record profits.

As travelers head to the airports this holiday season, those who haven’t flown for a while could be forgiven for wondering if the plane is a bit more cramped than they remembered.

For decades, airlines have worked to find new ways to fit as many seats as possible on their aircraft, a trend that hasn’t let up even as carriers are coming off a stretch of record profits that in 2016 totaled $13.5 billion industrywide.

But with labor costs rising and gas prices and airport fees steadily inching upward, the pressure is on to control expenses and keep revenue growing apace. Packing even a few more seats onto an aircraft is an efficient way to spread costs over more passengers and ideally earn a few more dollars per flight.

In September, American Airlines announced a plan to add as many as 12 seats to some of its single-aisle planes as part of an effort to standardize its seating layouts following its 2013 merger with US Airways. The added seat count is expected to generate as much as $500 million in revenue through 2021.

United Airlines has made similar changes after its merger with Continental Airlines, adding eight to 12 seats to its narrowbody aircraft.

For passengers, perhaps the most visible change over the years has been the steady decline of the space between a seat and the one in front of it, known in the industry as seat pitch. Whereas pitch of 34 to 35 inches was once common in coach seating on single-aisle jets, the norm for legacy carriers like American, Delta and United has settled between 30 and 31 inches.

Ultra-low-cost carriers like Spirit Airlines have pushed it as far as 28 inches between seats and aren’t shy about drawing a connection between the tighter layouts and their lower fares.

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Seats have also gotten narrower over time, dropping from as much as 20 inches in the 1990s to between 17 and 18 inches nowadays.

But the distance between seats tells only part of the story. Airlines have switched to a new generation of slimline seats, with new materials offering lighter, more compact cushioning that can give back as much as an inch of legroom for passengers.

"Seats themselves have gotten much thinner ... they're more ergonomic. You can put more seats on an airplane without necessarily taking as much space as people think you are," said Brett Snyder, author of the airline industry blog Cranky Flier and president of air travel assistance company Cranky Concierge. "Smarter, better design can account for a lot of this increase in density."

Carriers have also gotten creative with the layouts of galleys and more compact lavatories that can free up room for an extra row or two of seats.

Getting crowded

Factor in that more people than ever are traveling and planes are departing with average load factors — a measure of how full the plane is — of over 80 percent, and it’s easy to see why planes can feel more claustrophobic.

And the effect goes beyond just when you’re in your seat. More people aboard each plane means the gate area is more crowded and boarding takes longer, there’s less overhead bin space to go around and lines at the lavatory can back up.

Passengers — and their desire to get the cheapest fares possible — aren’t blameless in the current state of affairs. American has previously said that as many as 87 percent of its passengers fly the airline just once in a given year, with pricing being the major factor in where they decide to book.

In the early 2000s, American even rolled out a strategy to offer more legroom throughout coach and a marketing campaign to go with it, but backed off only a few years later amid disappointing returns.

“Customers have insisted that the one thing that’s more valuable than anything else is the cheapest possible ticket,” American’s former CEO Bob Crandall, who led the company from 1985 to 1998, said recently. “Well, if you want the cheapest possible ticket, you’re gonna have the smallest possible seat and the least possible facilities, because that’s how I get my costs down.”

The push back

There are signs that the push to add ever more seats to planes could be nearing a tipping point.

Earlier this year, reports leaked that American was planning to put three rows of seats with 29-inch pitch on its new Boeing 737 Max aircraft, new territory for a legacy airline that prompted backlash from employees and crew members.

The company ultimately backed off the plan, in part to spare flight attendants from having to explain to customers why their seat is tighter than other rows, CEO Doug Parker said.

“While we could convince ourselves that that might be able to produce somewhat higher revenues on the aircraft, what it was doing to our perception with our team wasn't worth it,” Parker said.

In July, a federal court ordered the Federal Aviation Administration to review seat size and legroom on airplanes — something that isn’t currently regulated, despite numerous congressional efforts — after a challenge from the advocacy group Flyers Rights.

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Proponents of regulating seat size have raised concerns that long periods of time seated in cramped confines could lead to medical issues, including potentially fatal deep vein thrombosis.

There are also worries that too-crowded airplanes could lead to problems in the case of an emergency evacuation.

But perhaps the biggest impetus to stopping the squeeze will come from business considerations, as airlines like American, Delta, United and even Southwest need to maintain some distance from their ultra-low-cost counterparts.

“If we get to a point where an American, a United or a Delta cabin feels like a Spirit or Frontier cabin, why am I going to pay to be on those airlines?” said George Ferguson, senior airlines analyst at Bloomberg Intelligence. “They still need to differentiate themselves so people understand what they’re getting.”